Air-conditioning equipment in vehicles form part of the prior art for the cooling, drying, heating and ventilation of vehicle interior compartments. The air is cooled and dried by means of refrigeration installations, while for heating purposes the cabin air is normally heated in heating heat exchangers which make the waste heat from the engine available. The cabin is ventilated by means of outside air or re-circulated air from the cabin via air blowers. Furthermore, the air-conditioning equipment is used to control the distribution of air in the cabin.
Refrigeration installations for the air-conditioning of a cabin in vehicles are known for cooling/drying and heating purposes. In these installations, a pressure which is supercritical with respect to the critical pressure in the circuit is generated on the high-pressure side of a vapor compression circuit, which includes a compressor, a gas cooler/condenser, an internal heat exchanger and a throttling device with at least one evaporator, which are connected in series, and form an integral, closed circuit for providing refrigeration or heating. In these installation, also a sub-critical pressure is reached on the low-pressure side of the circuit, while thermal energy is supplied to, or refrigeration energy is discharged from the refrigerant, which has been cooled on the low-pressure side, via the evaporator, and the refrigerant mass flow in the circuit is controlled by regulating it in the compressor (DE 44 322 72 C2). There is no configuration which relates to an incorporation of the installation in the air-conditioning unit of a vehicle with regard to the various operating modes of heating, cooling and drying.
DE 198 13 674 C1 describes a refrigeration installation with heat pump function which uses the refrigeration circuit to transfer heating capacity to the cabin air of vehicles. The objective in this case is to increase the efficiency of the heating immediately after the vehicle has been started up and to shorten its response time. This is achieved by using the refrigeration installation as a heat pump, with the heat being introduced into the refrigerant in the ambient heat exchanger using outside air and further heating being carried out in an exhaust-gas heat exchanger with the exhaust gases of an internal combustion engine. The refrigerant is subsequently compressed in the refrigerant compressor and cold vehicle interior compartment air which has been sucked in is conducted through the interior compartment heat exchanger. In this way, the vehicle interior compartment air is heated in the interior compartment heat exchanger, and, as a result, the vehicle cabin is heated. If the installation is used to cool and dry the vehicle interior compartment air, the interior compartment heat exchanger cools and dries the humid vehicle interior compartment air which has been sucked in. As a result, the vehicle interior compartment air is cooled, the water vapor contained in the air which has been sucked in is condensed and the vehicle cabin is air-conditioned.
This document does not solve the problem of the windows in the vehicle cabin fogging up when the refrigeration installation is switched from cooling and drying to heating.
DE 4318255 A1 describes a device for air-conditioning the interior compartment of a vehicle equipped with a drive which generates waste heat. This includes a refrigerant circuit and a heating-agent circuit, which can only be coupled in a heat-exchanging manner via at least one first heat exchanger. Whereas the heating-agent circuit includes a heat exchanger for capturing the waste heat from the drive unit and a heating heat exchanger arranged in the path of the air which is to be transported to the vehicle interior, the refrigerant circuit comprises, in the path of the air, an evaporator, a bypass passage and a waste-air passage leading to the latter and a waste-air port and also a refrigerant compressor. For cooling operation, a condenser and cooler can be integrated into the two circuits by means of switchover valves; the heating heat exchanger can also be disconnected by means of a valve-fitted bypass. The intention is to achieve various energy-saving air-conditioning objectives in the vehicle.
One drawback of these solutions is that the cabin air is not heated directly, but rather by means of a heating heat exchanger in the heat-transfer medium circuit as part of the engine cooling system. On account of the thermal masses involved, the inertia of the system is high, which has an adverse effect on the heating dynamics and is not compatible with traffic safety objectives.
DE 3907201 C2 discloses a motor vehicle equipped with an air-conditioning system which has a heating mode, i.e. it also acts as a heat pump. In order, in the heating mode, to prevent the uptake of moisture which may have precipitated in the evaporator in the preceding cooling mode by the air which is to be conditioned, various measures are proposed. For example, for the heating mode a separate heat exchanger is provided, and furthermore a moisture sensor may be arranged at the interior compartment heat exchanger, which, depending on the moisture level determined, either suppresses the heating mode or activates a dehumidification device provided downstream of the cooling evaporator for conditioning the air.
A drawback of one solution is that, under certain frequent vehicle operating conditions such as previous drying of the air for the vehicle cabin at outside temperatures of, for example, 0° C. to 10° C., heating operation is not possible or only a very limited capacity can be obtained from the installation. The other solution avoids the desirable continuous drying of air when utilizing the refrigeration installation in a heat pump mode and therefore does not comply with the requirements of keeping the windows in the vehicle cabin free of fogging, in particular in an air recirculation mode. Dehumidification devices based for example on adsorptive materials cause a pressure drop in the air mass flow for the ventilation of the vehicle cabin and have to be desorbed periodically. To achieve continuity in this case, it is necessary to provide at least two dehumidification devices between which it is possible to switch, which, in combination with electric heating and air delivery means as well as an outgoing flow for desorption, involves a considerable technical outlay.
EP 09 898 003 A2 describes a refrigeration circuit with a heat pump for use particularly in a vehicle which is not operated using an internal combustion engine. The system includes an air-conditioning device with two heat exchangers, through which refrigerant flows, a first condenser and an evaporator. In the air-conditioning unit, the heat exchanger arranged downstream with respect to the incoming cabin air is directly fluid-connected to the high-pressure side of the compressor, and, depending on the operating situation, hot refrigerant under a high pressure flows through it. For the required heating of the cabin, the interior compartment air flow is conducted through this component only when required. In the cooling and drying mode, the refrigerant flows from the compressor through the first condenser in the air-conditioning unit, is then cooled in the second condenser, expanded and liquefied in a throttling device and then, in order to take up heat for cooling the cabin air, passes into the evaporator. Accordingly, in a pure cooling mode, no air flows across the first condenser. In the cooling mode with reheating, as required for dehumidification, only a partial flow passes via this component. For dehumidification purposes, the refrigerant successively flows through the first condenser, through the second condenser, then, in liquefied form, through the throttling location into the evaporator, to the accumulator and back to the compressor. In all three operating modes (cooling, cooling and reheating and heating), all of the refrigerant is always passed first through the first condenser, then through the second condenser, the evaporator and via the accumulator, wherein different pressures and temperatures at different throttling locations can be set, to various bypass locations to configure the circuit in different ways.
Drawbacks are that a high thermal load is constantly introduced into the air-conditioning unit, the heating heat exchanger has to withstand high temperature and pressure loading, the piping of the installation in the vehicle is complex and takes up a considerable amount of space, there are avoidable pressure drops with a reduction in efficiency and a substantial amount of refrigerant is required. Therefore, the installation does not satisfy the general demands with regard to complexity, costs, efficiency, performance and ecological requirements.
The prior art therefore describes systems in which the refrigeration installation evaporator, i.e. the heat exchanger through which refrigerant flows, when the refrigeration installation is operating in the cooling mode, cools and dries the air entering the vehicle interior compartment, or, when the refrigeration installation is operating in the heating mode, heats the air which enters the vehicle interior. In the cooling mode, the water vapor in the air condenses at the cold surfaces of the heat exchanger. Therefore, in the heating mode, the water adhering to the surface of the heat exchanger through which the refrigerant flows may evaporate and humidify the air entering the vehicle interior. This can lead to increased fogging of the windows. To keep the windows free of such fogging, according to the prior art the incoming air mass flow is cooled at temperatures of approx. −4° C. and 10° C. by the refrigeration installation in the cooling mode, and is thereby dried, and is then heated in the heating heat exchanger to the required air temperature in what is known as the “reheat mode”. When the heat exchanger through which refrigerant flows is being used for heating purposes, the function of cooling and therefore drying cannot be performed simultaneously.
It is therefore an object of the present invention to reconfigure and extend an arrangement of components of a refrigeration installation in vehicles so as to improve the heating capacity in vehicles in all operating states, and allowing the refrigeration installation to be switched in any desired way between heating and cooling operation without the windows fogging up.
A second object of the present invention is to dry the air entering the vehicle interior even when the heat pump is operating and at outside temperatures which are well below those which are currently possible.
A third object of the invention is to maintain passenger comfort by storing heat (e.g. for heating and cooling purposes) in the event the engine is switched off for a brief period of time.